Does environmental heterogeneity affect species co‐occurrence in ecological guilds across stream macroinvertebrate metacommunities?

Null model analyses have greatly improved our understanding of species co‐occurrence. Null model analyses have shown, for example, that cold‐blooded animals show less segregated distributions than warm‐blooded animals. This topic has rarely been studied simultaneously across multiple metacommunities. We analysed data on 10 stream metacommunities (with 10 communities in each metacommunity) of a cold‐blooded animal group, benthic macroinvertebrates, and examined co‐occurrence within five ecological guilds. We found that the segregated species co‐occurrence was not the rule in stream invertebrate guilds. This was evidenced by the finding that only 10% of the 50 guild matrices we analyzed showed significant segregation and no matrices showed significant aggregation in the within‐stream analyses. However, in the across‐streams analysis, all guilds showed significant segregation. We neither found differences in the degree of segregation among the guilds, the degree of species segregation did not increase with overall environmental heterogeneity, and there were no differences in the relationships between species segregation and overall environmental heterogeneity among the guilds. Expanding the spatial extent from single stream metacommunities (i.e. within each stream) to the whole study region (i.e. across the streams) increased significantly segregation in all guilds. Because environmental heterogeneity across streams was much higher than within single streams, overall environmental heterogeneity may nevertheless have effects on species segregation. It also seems that the effects of overall heterogeneity on species segregation were masked by mass effects in the within‐stream analyses.     

Spatial and temporal organisation of the pre-dispersal seed predator guild in a perennial legume, Vicia tenuifolia

Abstract.  1. The variability of species combinations and membership assembly patterns in an insect pre-dispersal seed predator guild were studied at various spatial and temporal resolutions using presence/absence and abundance data in null models. The guild consists of seven beetle species (four bruchids and three curculionids) and one moth species that live on a perennial vetch, Vicia tenuifolia Roth (Leguminosae).
2. The seed predator guild varied considerably in the number of members and species combinations in space and time, and, contrary to expectations, there was no evidence of interspecific competition among guild members, supporting the view that other processes, including chance events, could contribute to guild formation.
3. It is concluded that, apart from the possibility of stochastic co-occurrence, it is the narrow host specialisation that constrains seed predator members to participate in the guild, and small differences in habitat preference can also lead to spatial and temporal variation.     

Species richness at the guild level: effects of species pool and local environmental conditions on stream macroinvertebrate communities

1.?A fundamental question in ecology is which factors determine species richness. Here, we studied the relative importance of regional species pool and local environmental characteristics in determining local species richness (LSR). Typically, this question has been studied using whole communities or a certain taxonomic group, although including species with widely varying biological traits in the same analysis may hinder the detection of ecologically meaningful patterns. 2.?We studied the question above for whole stream macroinvertebrate community and within functional feeding guilds. We defined the local scale as a riffle site and the regional scale (i.e. representing the regional species pool) as a stream. Such intermediate-sized regional scale is rarely studied in this context. 3.?We sampled altogether 100 sites, ten riffles (local scale) in each of ten streams (regional scale). We used the local-regional richness regression plots to study the overall effect of regional species pool on LSR. Variation partitioning was used to determine the relative importance of regional species pool and local environmental conditions for species richness. 4.?The local-regional richness relationship was mainly linear, suggesting strong species pool effects. Only one guild showed some signs of curvilinearity. However, variation partitioning showed that local environmental characteristics accounted for a larger fraction of variance in LSR than regional species pool. Also, the relative importance of the fractions differed between the whole community and guilds, as well as among guilds. 5.?This study indicates that the importance of the local and regional processes may vary depending on feeding guild and trophic level. We conclude that both the size of the regional species pool and local habitat characteristics are important in determining LSR of stream macroinvertebrates. Our results are in agreement with recent large-scale studies conducted in highly different study systems and complement the previous findings by showing that the interplay of regional and local factors is also important at intermediate regional scales.     

An Ant Mosaic Revisited: Dominant Ant Species Disassemble Arboreal Ant Communities but Co-Occur Randomly

The spatial distributions of many tropical arboreal ant species are often arranged in a mosaic such that dominant species have mutually exclusive distributions among trees. These dominant species can also mediate the structure of the rest of the arboreal ant community. Little attention has been paid to how diet might shape the effects of dominant species on one another and the rest of the ant community. Here, we take advantage of new information on the diets of many tropical arboreal ant species to examine the intra- and inter-guild effects of dominant species on the spatial distribution of one another and the rest of the tropical arboreal ant community in a cocoa farm in Bahia, Brazil. Using null model analyses, we found that all ant species, regardless of dominance status or guild membership, co-occur much less than expected by chance. Surprisingly, the suite of five dominant species showed random co-occurrence patterns, suggesting that interspecific competition did not shape their distribution among cocoa trees. Across all species, there was no evidence that competition shaped co-occurrence patterns within guilds. Co-occurrence patterns of subordinant species were random on trees with dominant species, but highly nonrandom on trees without dominant species, suggesting that dominant species disassemble tropical arboreal ant communities. Taken together, our results highlight the often complex nature of interactions that structure species-rich tropical arboreal ant assemblages.     

Detecting signatures of competition from observational data: a combined approach using DNA barcoding,diversity partitioning and checkerboards at small spatial scales

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Inter- and intra-guild patterns of food resource utilization by chironomid larvae in a subtropical coastal lagoon

Studies on food preferences provide background information on the mechanisms that allow coexistence and resource exploitation among several species within the same system. In this study, we aimed to identify the trophic guild of chironomid larvae based on their feeding habits using gut content analysis. Larvae were collected using an Eckman-Birge grab in many areas of the subtropical Peri lagoon (southern Brazil) seasonally between March 2008 and April 2009. Null models were used to determine the frequency of co-occurrence of food items in the diets of chironomid larvae and to determine the frequency of co-occurrence of species belonging to a particular guild. Significant differences (seasonal or annual) were observed in patterns of co-occurrence of food items in the larval diets. Animal remains had a lower co-occurrence than would be expected as a result of chance, and plant items had a co-occurrence greater than would be expected by chance. The c scores for co-occurrence of species belonging to both predator and herbivore guilds revealed a higher co-occurrence of species than would be expected by chance. We suggest that the factors responsible for the results of this study were resource partitioning among species, habitat heterogeneity and resource availability in the environment.     

Insect guild structure associated with eastern hemlock in the southern Appalachians

An assessment of the insect guild structure associated with immature and mature eastern hemlock, Tsuga canadensis (L.) Carrière, at high and low elevations was made before the invasion by the hemlock woolly adelgid, Adelges tsugae (Annand), and elongate hemlock scale, Fiorinia externa Ferris. Guild dynamics were determined among 243 insect species associated with eastern hemlock in the southern Appalachians. Detritivore, hematophage, herbivore, fungivore, parasitoid, predator, scavenger, and transient guild assignments were made. The herbivore and transient guilds were subdivided into chewers, sapsuckers, flower feeders, pollen feeders, pollen/nectar/sap feeders, and seed feeders. A significant association was found between guilds on immature and mature hemlocks at low elevations, but no significant association was found at high elevations. There was also a strong association of phytophagous insects on immature hemlocks and scavengers on mature hemlocks. The observed transient, scavenger, and predator guilds had a significantly lower co-occurrence among species indicating segregation of the species within these guilds. The herbivore guild had a significantly higher co-occurrence among species than the simulated index indicating aggregation of species within this guild across sites. Detritivore, hematophage, and parasitoid guilds did not differ significantly from the simulated community. These results document a diverse and dynamic insect community on eastern hemlock before invasion by hemlock woolly adelgid and elongate hemlock scale.     

Diatom ecological guilds display distinct and predictable behavior along nutrient and disturbance gradients in running waters

Three diatom ecological guilds were distinguished based on their potential to tolerate nutrient limitation and physical disturbance, i.e. a low profile, high profile, and motile guild. The guild distributions were examined along nutrient and flow disturbance gradients and across habitats in two extensively sampled streams. The guilds showed distinct distributional patterns, i.e. the low profile guild was favored in nutrient-poor and high disturbance habitats; the high profile guild reached a maximum in nutrient-rich sites and in conditions of low flow disturbance; and the motile guild increased along the nutrient gradients and decreased along the disturbance gradient. Guild distribution was habitat-specific: the low profile guild dominated the epipsammon, the high profile guild showed preference for epilithon and epiphyton, and the motile guild—for epipelon. The highest guild diversity was observed at high nutrient levels across all habitats, at higher flow disturbance levels, and in the epipelon and epiphyton. Comparisons of species, guild, and environmental distances, derived from species counts, guild abundance, and physico-chemical data, respectively, revealed high congruence between species–environment and guild–environment correlations. The predictable behavior of the three ecological guilds along nutrient and disturbance gradients, and across major benthic habitats elucidates the functional value of different diatom growth morphologies in species–environment interactions and suggests a potential use in ecological assessments of human-impacted ecosystems.     

Differences in functional trait responses to elevation among feeding guilds of Aculeata community

The response of communities to environmental change is expected to vary among feeding guilds. To evaluate the response of guilds to environmental factors without considering the taxonomic specificities, it is useful to examine Aculeata bees and wasps, which consist of closely related taxa including different guilds, pollinators, predators, and parasitoids. In this study, we evaluated changes in species diversity (SD) and functional traits of each feeding guild along an elevational gradient in a boreal forest in northern Japan. We used yellow pan traps to collect Aculeata bees and wasps at 200–1600 m above sea level. We investigated six functional traits (trophic level, seasonal duration, body size, elevational range, nesting position, and soil dependency) and the horizontal distribution of the species. The SD of all Aculeata, predators, and parasitoids decreased with an increase in elevation; however, the SD of pollinators did not show any specific trend. Although the functional trait composition of all Aculeata species did not show any trend, that of each feeding guild responded to elevation in different ways. Pollinators increased in body size and showed a decrease in seasonal duration with increasing elevation, suggesting that tolerance and seasonal escape from physical stress at high elevations are important for shaping pollinator communities. Predators increased their elevational range and the proportion of above‐ground nesting species increased with increasing elevation, suggesting that the ability to live in a wider range of environments and avoid unsuitable soil environments at high elevations might be important. Parasitoids changed their hosts and displayed variable traits with increasing elevation, suggesting that brood parasitoids have difficulty in surviving at high elevation. The traits for each guild responded in different ways, even if they were dominated by the same environmental factors. Our findings imply that differences in the responses of functional traits would produce different community assembly patterns in different guilds during further climate change.     

Guild structure of carnivorous intertidal fishes of the Chilean coast: implications of ontogenetic dietary shifts

Although ontogenetic changes in resource use within species are common in animals, these changes have not been widely considered in studies of guild structure within communities. The occurrence of one or more shifts in resource use in an individual of a given species during its life should mean that it would also belong to different guilds at different life stages. We specifically addressed this issue by describing the feeding habits of ten species of carnivorous fishes occurring in tidepools in rocky intertidal areas along the coast of central Chile. Most of these species undergo clear ontogenetic dietary shifts and a feeding guild structure of this group of fishes was established that takes these dietary shifts into account. Each species was divided into a number of size classes. Dietary overlap values between both intraspecific and interspecific size-class pairs in the entire group of ten species were used to construct a phenogram of dietary similarity through an UPGMA cluster analysis. Numbers of guilds and their memberships were established objectively by applying a bootstrapping procedure. Four “ontogenetic” feeding guilds (OFGs), each consisting of size-classes of species, were recognized. The majority of species belonged to more that one guild. Interestingly, when the bootstrapping procedure was applied to a phenogram based on the diets of “taxonomic” or complete species, only one significant guild was found. The implications of these ontogenetic dietary shifts for interspecific interactions are substantial because the identity of the species with which each fish species shares resources change through their lives. The usefulness of taxonomic species for investigating potential competitive interactions in this assemblage is greatly undermined. Received: 26 September 1997 / Accepted: 15 December 1997     

Guild structure of arthropods from Bornean rain forest trees

ABSTRACT. 1. 23275 arthropods collected by insecticide fogging from ten Bornean lowland rain forest trees were sorted to approximately 3000 species and assigned to guilds using two sets of criteria.
2. The rank order for proportions of guilds of species but not individuals is similar in tropical and temperate canopy samples.
3. Misplacement in the guild assignments of a few species can cause important differences in the proportions of certain guilds. This can seriously affect the results of comparisons of different samples, and views on proportional constancy of guilds of species on different trees.
4. Guilds of arthropod species such as chewers, suckers, all phytophages, predators, ants and tourists, occur in constant proportions in samples from different tropical trees and this constancy of proportion is similar in samples from groups of'closely related'and'distantly related'trees.
5. The guild concept of community structure and problems in assigning species to guilds are considered with respect to arthropod samples. The conclusions on constancy of proportion for guilds of species are tempered by remarks on the problems of guild composition.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.     

Competition can lead to unexpected patterns in tropical ant communities

Ecological communities are structured by competitive, predatory, mutualistic and parasitic interactions combined with chance events. Separating deterministic from stochastic processes is possible, but finding statistical evidence for specific biological interactions is challenging. We attempt to solve this problem for ant communities nesting in epiphytic bird’s nest ferns (Asplenium nidus) in Borneo’s lowland rainforest. By recording the frequencies with which each and every single ant species occurred together, we were able to test statistically for patterns associated with interspecific competition. We found evidence for competition, but the resulting co-occurrence pattern was the opposite of what we expected. Rather than detecting species segregation—the classical hallmark of competition—we found species aggregation. Moreover, our approach of testing individual pairwise interactions mostly revealed spatially positive rather than negative associations. Significant negative interactions were only detected among large ants, and among species of the subfamily Ponerinae. Remarkably, the results from this study, and from a corroborating analysis of ant communities known to be structured by competition, suggest that competition within the ants leads to species aggregation rather than segregation. We believe this unexpected result is linked with the displacement of species following asymmetric competition. We conclude that analysing co-occurrence frequencies across complete species assemblages, separately for each species, and for each unique pairwise combination of species, represents a subtle yet powerful way of detecting structure and compartmentalisation in ecological communities.     

Influence of body size on coexistence of bird species

Theory suggests that body size is an important factor in determining interspecific competition and, ultimately, in structuring ecological communities. However, there is a lack of pragmatic studies linking body size and interspecific competition to patterns in ecological communities. The objective of the present study was to determine the effect of body size (mass) on competitive interactions between bird pairs and to investigate the influence of food guilds. Point-counts were carried out in nine sites every month from November 2002 to November 2003 in the Cuetzalan Region, Mexico, and we used presence/absence and abundance data for the analyses. To calculate the strength of competition we used the Angle Frequency Method to extract form factors from 20 pairwise interactions. A prototype competition interaction and random pairs were also constructed. We used clustering techniques (PCA) to calculate the dissimilarity scores (distances, D) of each of the pairwise interactions to the prototype competition and random pairs and one-way ANOVA to test for differences between the means of the random and competitive pairs. The ratio in body mass (lnBM) for each of the interacting pairs was calculated, and the association between the lnBM ratio and the strength of competition (D) was tested using a Pearson product-moment correlation coefficient. To test for the influence of foraging guilds we used a univariate general linear model. Our results demonstrate a significant negative relationship between bird body mass ratio and competition strength – i.e. competition strength increased when the body masses of the birds became more similar. We did not find a significant influence of foraging guild on the relationship between body mass ratio and competition strength. On the basis of these results, we suggest that high variation in body sizes amongst sympatric species promotes coexistence in communities.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Different responses of avian feeding guilds to spatial and environmental factors across an elevation gradient in the central Himalaya

Although elevational patterns of species richness have been well documented, how the drivers of richness gradients vary across ecological guilds has rarely been reported. Here, we examined the effects of spatial factors (area and mid‐domain effect; MDE) and environmental factors, including metrics of climate, productivity, and plant species richness on the richness of breeding birds across different ecological guilds defined by diet and foraging strategy. We surveyed 12 elevation bands at intervals of 300 m between 1,800 and 5,400 m a.s.l using line‐transect methods throughout the wet season in the central Himalaya, China. Multiple regression models and hierarchical partitioning were used to assess the relative importance of spatial and environmental factors on overall bird richness and guild richness (i.e., the richness of species within each guild). Our results showed that richness for all birds and most guilds displayed hump‐shaped elevational trends, which peaked at an elevation of 3,300–3,600 m, although richness of ground‐feeding birds peaked at a higher elevation band (4,200–4,500 m). The Normalized Difference Vegetation Index (NDVI)—an index of primary productivity—and habitat heterogeneity were important factors in explaining overall bird richness as well as that of insectivores and omnivores, with geometric constraints (i.e., the MDE) of secondary importance. Granivore richness was not related to primary production but rather to open habitats (granivores were negatively influenced by habitat heterogeneity), where seeds might be abundant. Our findings provide direct evidence that the richness–environment relationship is often guild‐specific. Taken together, our study highlights the importance of considering how the effects of environmental and spatial factors on patterns of species richness may differ across ecological guilds, potentially leading to a deeper understanding of elevational diversity gradients and their implications for biodiversity conservation.     

Metacommunity patterns of highly diverse stream midges: gradients,chequerboards, and nestedness,or is there only randomness?

Abstract.  1. Several non-random patterns in the distribution of species have been observed, including Clementsian gradients, Gleasonian gradients, nestedness, chequerboards, and evenly spaced gradients. Few studies have examined these patterns simultaneously, although they have often been studied in isolation and contrasted with random distribution of species across sites.
2. This study examined whether assemblages of chironomid midges exhibit any of the idealised distribution patterns as opposed to random distribution of species across sites within the metacommunity context in a boreal drainage system. Analyses were based on stream surveys conducted during three consecutive years. Analytical approaches included ordinations, cluster analysis, null models, and associated randomisation methods.
3. Midge assemblages did not conform to Clementsian gradients, which was evidenced by the absence of clearly definable assemblage types with numerous species exclusive to each assemblage type. Rather, there were signs of continuous Gleasonian variability of assemblage composition, as well as significant nested subset patterns of species distribution.
4. Midge assemblages showed only weak relationships with any of the measured environmental variables, and even these weak environmental relationships varied among years.
5. Midge assemblages did not appear to be structured by competition. This finding was somewhat problematic, however, because the two indices measuring co-occurrence provided rather different signs of distribution patterns. This was probably a consequence of how they actually measure co-occurrence.
6. Although midge assemblages did not show a perfect match with any of the idealised distribution patterns, they nevertheless showed a resemblance to the empirical patterns found previously for several plant and animal groups.     

Effects of habitat characteristics and interspecific interactions on co-occurrence patterns of saproxylic beetles breeding in tree boles after forest fire: null model analyses

It is often suggested that habitat attributes and interspecific interactions can cause non-random species co-occurrence patterns, but quantifying their contributions can be difficult. Null models that systematically exclude and include habitat effects can give information on the contribution of these factors to community assembly. In the boreal forest, saproxylic beetles are known to be attracted to recently burned forests where they breed in dead and dying trees. We examined whether species co-occurrences of saproxylic beetles that develop in, and emerge from, boles of recently burned trees show non-random patterns. We also estimated the extent to which both the post-fire habitat attributes and interspecific interactions among beetles contribute to such patterns. We sampled tree boles encompassing key attributes (tree species, tree size/dbh and burn severity) that are thought to characterize species–habitat associations of saproxylic beetles, a proposition that we tested using indicator species analysis. Two null models with no habitat constraints (“unconstrained”) indicated that a total of 29.4% of the species pairs tested had significant co-occurrence patterns. Habitat-constrained null models indicated that most of the detected species aggregations (72%) and segregations (59%) can be explained by shared and distinct species–habitat relationships, respectively. The assembly pattern was also driven by interspecific interactions, of which some were modulated by habitat; for example, predator and prey species tended to co-occur in large-sized trees (a proxy of available bark/wood food resource primarily for the prey). In addition, some species segregation suggesting antagonistic, competitive, or prey–predator interactions were evident after accounting for the species’ affinities for the same tree species. Overall, our results suggest that an intimate link between habitat and interspecific interactions can have important roles for community assembly of saproxylic assemblages even following disturbance by fire. We also show that a systematic application of null models can offer insight into the mechanisms behind the assembly of ecological communities.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Spatial and temporal variations among fish with similar strategies: patterns of reproductive guilds in a floodplain

Seasonal flooding regimes are closely related to the life history of neotropical fish, especially with regard to their reproduction. The classification of fish into reproductive guilds serves to identify broad patterns in reproductive types, which are important in developing management and conservation measures. We tested the hypothesis that the fish reproductive guilds in the Upper Paraná River floodplain exhibit spatial and temporal distributions. Samples were taken each quarter in 2010 from several environments (i.e., biotopes) and rivers of the plain. Fish were categorized into four reproductive guilds based on migration, external fertilization, and parental care. Moreover, the abundance and species richness within each guild were used to evaluate their patterns. Guilds were spatially structured, possibly due to species dispersion as well as the influence of the hydrological and limnological characteristics of the biotopes and rivers of the plain. The Paraná River presented lower analyzed metric values, which demonstrates the negative effects of the dam built upstream of the study area. The guilds also presented temporal structure. During the flood season, the guilds presented similar spatial structures, and the local environmental characteristics led to spatial differentiation in the structure of guilds (i.e., flooding promoted the homogenization of the reproductive guilds).